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1. Field of the Invention
The present invention relates to a method for cleaning surfaces of a surface finished article of manufacture to remove contaminants using continuous ultraviolet light and ozone. In addition, the combination of ozone and UV light can be used to remove the contaminants from the surface. The treatment enhances surface activation, allows for surface cleaning in short time periods and increases the wetting characteristics of the surface.
2. Description of Related Art
Surfaces of articles of manufacture always contain undesirable organic contaminant materials that prevent binding to the surfaces and which particularly reduce adhesion of a paint or film to the surfaces. Hence, surface preparation, which includes cleaning of the surfaces, of polymeric, polymer composite or metal substrates, to remove the organic contaminants is carried out prior to applying protective paint films or adhesive bonding. Surface preparation determines the mechanical and durability characteristics of the layered composite created. Currently the techniques used for surface preparation are mechanical surface treatments (e.g. abrasion), solvent wash and chemical modification techniques like corona, laser plasma, flame treatment and acid etching. Each of the existing processes have shortcomings and thus, they are of limited use. Abrasion techniques are found to be time consuming, labor intensive and have the potential to damage the adherent surface. Use of organic solvents results in volatile organic chemical (VOC) emissions. Chemical techniques are costly, are of limited use with regard to treating three dimensional parts, can be limited to a batch process (such as plasma, laser and acid etching) and need tight control.
The focused beams of the lasers make it difficult to treat a large surface. U.S. Pat. No. 4,803,021 to Werth et al describes such a method. U.S. Pat. No. 4,756,765 to Woodroffe describes paint removal with surface treatment using a laser.
Plasma treatment of surfaces requires relatively expensive equipment and the plasmas are difficult to control. The surfaces are treated with vaporized water in the plasma. Illustrative of this art are U.S. Pat. Nos. 4,717,516 to Isaka et al., 5,019,210 to Chou et al., and 5,357,005 to Buchwalter et al.
A light based process which cleans a substrate surface also creates a beneficial chemistry on the surface for adhesive bonding and paintability is described in U.S. Pat. No. 5,512,123 to Cates et al. The process involves exposing the desired substrate surface to be treated to flashlamp radiation having a wavelength of 160 to 5000 nanometers. Ozone is created from oxygen in the air by the short wavelength UV light or may be added with an ozone generator and combined with the UV light to increase the surface energy and wettability of the surface of the substrate being treated. Surfaces of substrates such as metals, polymers, polymer composites are cleaned by exposure to the flashlamp radiation. The problem with the Cates et al process is that the surface of the substrate is heated to a relatively high temperature, particularly by radiation above 500 nanometers and relatively long treatment times. Related patents to Cates et al are U.S. Pat. Nos. 3,890,176 to Bolon, 4,810,434 to Caines; 4,867,796 to Asmus et al; 5,281,798 to Hamm et al and 5,500,459 to Hagemeyer et al and U.K. Patent No. 723,631 to British Cellophane. Non-patent references are: Bolon et al., xe2x80x9cUltraviolet Depolymerization of Photoresist Polymersxe2x80x9d, Polymer Engineering and Science, Vol. 12 pages 109-111 (1972). M. J. Walzak et al., xe2x80x9cUV and Ozone Treatment of Polypropylene and poly(ethylene terephthalate)xe2x80x9d, In: Polymer Surface Modification: Relevance to Adhesion, K. L. Mittal (Editor), 253-272 (1995); M. Strobel et al., xe2x80x9cA Comparison of gas-phase methods of modifying polymer surfacesxe2x80x9d, Journal of Adhesion Science and Technology, 365-383 (1995); N. Dontula et al., xe2x80x9cA study of polymer surface modification using ultraviolet radiationxe2x80x9d, Proceedings of 20th Annual Adhesion Society Meeting, Hilton Head, S.C. (1997); C. L. Weitzsacker et al., xe2x80x9cUtilizing X-ray photoelectron spectroscopy to investigate modified polymer surfacesxe2x80x9d, Proceedings of 20th Annual Adhesion Society Meeting, Hilton Head, S.C. (1997); N. Dontula et al., xe2x80x9cUltraviolet light as an adhesive bonding surface pretreatment for polymers and polymer compositesxe2x80x9d, Proceedings of ACCE""97, Detroit, Mich.; C. L. Weitzsacker et al., xe2x80x9cSurface pretreatment of plastics and polymer composites using ultraviolet lightxe2x80x9d, Proceedings of ACT""97, Detroit, Mich.; N. Dontula et al., xe2x80x9cSurface activation of polymers using ultraviolet activationxe2x80x9d, Proceedings of Society of Plastics Engineers ANTEC""97, Toronto, Canada. Haack, L. P., et al., 22nd Adhesion Soc. Meeting (Feb. 22-24, 1999).
Non-pulsed UV lamps have been used by the prior art. These are described in: xe2x80x9cExperimental Methods in Photochemistryxe2x80x9d, Chapter 7, pages 686-705 (1982). U.S. Pat. No. 5,098,618 to Zelez is illustrative of the use of these types of lamps with a low wattage input.
There is a need for development of an environmentally friendly, as well as cost effective and robust surface treatment process for removing mold organic material contaminants from surfaces.
It is therefore an object of the present invention to provide a process which is reliable and which cleans surfaces of organic material contaminants. It is further an object of the present invention to provide a process which is rapid and economical. These and other objects will become increasingly apparent by reference to the following description and the drawings.
The present invention relates to a method for cleaning a finished surface of an article of manufacture which comprises:
exposing a contaminant on the surface to ultraviolet light in either continuous or pulsed form, to volatilize the organic material and thereby clean the surface without damaging the finished material surface. The wattage input to the lamp is between about 0.5 and 20 kW to provide continuous or pulsed light.
The substance and advantages of the present invention will become increasingly apparent by reference to the following drawings and the description.